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Heterocyclic Digallanates, Encapsulation of Lithium Cations in Organometallic Cages and C–H Bond Activation
Author(s) -
Uhl Werner,
Hentschel Anne,
Kovert Dirk,
Kösters Jutta,
Layh Marcus
Publication year - 2015
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201500207
Subject(s) - chemistry , intramolecular force , gallium , dimethoxyethane , crystal structure , agostic interaction , medicinal chemistry , geminal , hydrogen bond , crystallography , toluene , stereochemistry , molecule , metal , organic chemistry , electrode , electrolyte
Hydrogallation of the dialkynylbenzenes 1,3‐(R 2 R′Si‐C≡C) 2 C 6 H 4 ( 3 : R = Me, R′ = Ph; 4 : R = Ph, R′ = Me) with dichlorogallane, H‐GaCl 2 , afforded the corresponding dialkenylbenzenes 5 and 6 , with GaCl 2 groups geminal to the silyl substituents. Compound 6 was characterised by crystal structure determination, which revealed intramolecular bridging of both gallium atoms by two chlorine atoms as a new structural motif. Treatment of 5 and 6 with six equivalents of ethyllithium gave unprecedented heterocyclic digallanates 7 and 8 , in which two four‐coordinate gallium atoms were bridged by two 1,3‐dialkenylbenzene spacer ligands. The obtained large heterocycles encapsulated two lithium counterions in their molecular cavities. The lithium atoms were coordinated in a cryptand‐like fashion and showed a variety of short contacts to aromatic rings, alkenyl groups, and α‐carbon atoms of terminal ethyl groups. They could be removed from the molecular cavity by coordination with chelating 1,2‐dimethoxyethane ligands. Heating of digallanates 7 and 8 in toluene to more than 100 °C over a period of 5 h resulted in fascinating transformations with C–H bond activation and ortho ‐metallation. Five‐membered GaC 4 metallacycles were formed, which had a terminal R 2 R′Si‐CH=CH‐ group resulting from the formal protolytic cleavage of an alkenyl–gallium bond by the ortho ‐hydrogen atom.